The present invention relates generally to laser hardened materials and structures, and more particularly to a novel optical filter structure for selectively blocking laser radiat:on within a predetermined wavelength band while passing radiation of other wavelengths.
Optical switching devices comprising transition or switching materials which are optically transparent in one state but which transform to an opaque metallic state when heated to a characteristic transition temperature are well developed for applications such as optical filters, modulators, laser output couplers and the like. These devices are generally characterized by a transition from substantial transparency below the characteristic transition temperature to substantial opacity above that temperature, at all wavelengths.
The invention provides a substantially improved optical absorption band filter capable of actively or passively blocking light of wavelength equal to or shorter than a predetermined design wavelength while passing wavelengths longer than the design wavelength. The invention is an optical high-pass filter which becomes absorptive upon being cooled to an insulating-to-superconducting transition temperature T.sub.c, or is driven to the transmissive state by heating. The filter comprises insulating-to-superconducting transition material in granular form dispersed in a dielectric host material of substantially any shape. In the low temperature state, the resonant absorption is provided by the dielectric anomaly described by the Maxwell-Garnett theory. The invention therefore is a substantial improvement over the totally opaque switching reflection filter, the non-switching metallic array filter, the fixed wavelength switching element reflection band filter, and other wavelength responsive laser hardening devices.
It is, therefore, a principal object of the invention to provide an improved optical filter.
It is a further object of the invention to provide an optical filter for blocking laser radiation at and shorter than a preselected wavelength while passing radiation at longer wavelengths.
It is yet another object of the invention to provide an optical filter having fast response time.
It is another object of the invention to provide an optical filter having a curved structure or other shaped configuration
It is another object of the invention to provide an optical filter for actively or passively absorbing a preselected wavelength range.
It is a further object of the invention to provide a switchable filter incorporating insulating-to-superconducting materials to provide selective wavelength filtering.
It is a further object of the invention to provide an optical filter which is switchable at preselected temperature, has low absorption losses prior to switching, and is independent of impinging radiation prior to switching.
These and other objects of the invention will become apparent as the description of representative embodiments proceeds